Thermography is an image-forming process including a heating step and hence includes photothermography in which the image-forming process includes image-wise exposure and direct thermal processes in which the image-forming process includes an image-wise heating step. In direct thermal printing a visible image pattern is produced by image-wise heating of a recording material.
U.S. Pat. No. 4,378,424 discloses in a heat developable and heat stabilizable photographic silver halide element comprising a support having thereon, in reactive association, in binder: (a) photographic silver halide, (b) a photographic silver halide developing agent, (c) an activating concentration of a thermal base releasing compound, the improvement comprising (d) a stabilizing concentration of a mesoionic 1,2,4-triazolium-3-thiolate silver halide stabilizer.
U.S. Pat. No. 4,351,896 discloses in a heat developable and heat stabilizable photographic silver halide element comprising a support having thereon, in reactive association, in binder: (a) photographic silver halide, (b) a photographic silver halide developing agent, (c) an activating concentration of a thermal base releasing compound, the improvement comprising (d) a stabilizing concentration of a mesoionic 1,2,4-triazolium-3-thiolate silver halide stabilizer precursor containing a heat releasable blocking group on the sulfur atom.
U.S. Pat. No. 4,404,390 discloses a mesoionic 1,2,4-triazolium-3-thiolate precursor represented by the formula:
wherein: R1 is alkyl containing 1 to 18 carbon atoms, —N(—R6)R5, alkenyl containing 3 to 18 carbon atoms, cycloalkyl containing 3 to 12 carbon atoms, or aryl containing 6 to 20 carbon atoms; R2 is alkyl containing 1 to 9 carbon atoms or aryl containing 6 to 12 carbon atoms; R3 is alkyl containing 1 to 18 carbon atoms, aryl containing 6 to 20 carbon atoms, or cycloalkyl containing 3 to 12 carbon atoms; R4 is carboxyaryl containing 7 to 13 carbon atoms, cyano (CN) or amido (CONH2); R5 and R6 are individually hydrogen, alkyl containing 1 to 18 carbon atoms, or aryl containing 6 to 20 carbon atoms, provided that when one of R5 and R6 is alkyl then both R5 and R6 are alkyl; n is 1 or 2; and X is an acid anion.
U.S. Pat. No. 4,351,896 and U.S. Pat. No. 4,404,390 disclose mesionic silver halide stabilizer precursors, which upon thermal processing form a stabilizer moiety which reacts with the silver halide in unexposed areas to form a stable silver (I) salt. However, U.S. Pat. No. 4,351,896 and U.S. Pat. No. 4,404,390 are silent in respect of their use in substantially light-insensitive thermographic recording-materials whose thermosensitive element contains a substantially light-insensitive organic silver salt and a reducing agent therefor.
U.S. Pat. No. 4,411,984 in a photographic element comprising a support having thereon, in reactive association, in binder, photographic silver halide and a dye precursor, the improvement wherein, said dye precursor is a diphenylamine having, in an ortho position to the amine, a sulfonyldiamido group that is capable upon oxidation of said diphenylamine of releasing a sulfonylamine fragment which, in turn, is capable of thermally releasing ammonia or an amine and wherein said diphenylamine is capable upon oxidation of forming a phenazine dye. U.S. Pat. No. 4,404,390 further discloses 1,5-dimethyl-6-allyl-1,2,4-triazolium-3-thiolate as a development accelerator in the photographic element.
JP 05-107764 discloses a silver halide photosensitive material capable of stably giving a high density image with low fog independently of a change in processing conditions and inhibiting the lowering of the sensitivity during storage in the raw state, the photosensitive material comprising a polymerizable photosensitive layer containing silver halide, a reducing agent and a polymerizable compound formed on a substrate, a mesoionic compound represented by the formula is incorporated into the photosensitive polymerizable layer:
wherein G is a 5- or 6-membered ring having N, O, S and/or Se as a hetero atom, E is —O—, —S— or —N-D (where D is alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, aryl or a heterocyclic group) and G may have a substituent. JP 05-107764 further discloses that the mesoionic compound is a compound represented by formula (II):
wherein D1 is an alkyl, cycloalkyl, alkynyl, aralkyl, aryl or heterocyclic group; D2 is a hydrogen atom or an alkyl, cycloalkyl, alkeynyl, aralyly, aryl or heterocyclic group; L is —O—, —S—, or —N(D3)-; and D3 is an alkyl, cycloalkyl, alkynyl, aralkyl, aryl or heterocyclic, amino, acylamino, sulfonamido, ureido or sulfamoylamino; and D1 and D2 and D2 and D3 may represent the atoms needed to form a ring.
EP-A 0 713 133 discloses a thermal imaging system consisting of (i) a donor element comprising on a support a donor layer containing a binder and a thermotransferable reducing agent capable of reducing a silver source to metallic silver and (ii) a receiving element comprising on a support a receiving layer comprising a silver source, capable of being reduced by means of heat in the presence of a reducing agent, a binder and a stabiliser selected from the group consisting of benzotriazoles, heterocyclic mercaptanes, sulphinic acids, 1,3,4-triazo-indinolines, 1,3-dinitroaryl compounds, 1,2,3-triazoles, phthalic acids and phthalic acid derivatives.
EP-A 0 901 040 discloses a substantially light-insensitive monosheet recording material comprising a support and a thermosensitive element containing a substantially light-insensitive organic silver salt, an organic reducing agent therefor in thermal working relationship therewith and a binder, characterized in that said thermosensitive element further contains an unsaturated carbocyclic or heterocyclic stabilizer compound substituted with a—SA group where A is hydrogen, a counterion to compensate the negative charge of the thiolate group or a group forming a symmetrical or an asymmetrical disulfide and said recording material is capable of producing prints with a numerical gradation value defined as the quotient of the fraction (2.5-0.1)/(E2.5-E0.1) greater than 2.3, where E2.5 is the energy in Joule applied in a dot area of 87 μm×87 μm of the imaging layer that produces an optical density value of 2.5, and E0.1 is the energy in Joule applied in a dot area of the imaging layer material that produces an optical density value of 0.1.
WO 94/16361 discloses a multilayer heat-sensitive material which comprises: a color-forming layer comprising: a color-forming amount of finely divided, solid colorless noble metal or iron salt of an organic acid distributed in a carrier composition; a color-developing amount of a cyclic or aromatic organic reducing agent, which at thermal copy and printing temperatures is capable of a color-forming reaction with the noble metal or iron salt; and an image-toning agent; characterized in that (a) the carrier composition comprises a substantially water-soluble polymeric carrier and a dispersing agent for the noble metal or iron salt and (b) the material comprises a protective overcoating layer for the color-forming layer. Furthermore, WO 94/16361 discloses that suitable antifoggants are well-known photographic anti-foggants such as mercaptobenzotriazole, chromate, oxalate, citrate, carbonate, benzotriazole (BZT), 5-methylbenzotriazole, 5,6-dimethylbenzotriazole, 5-bromobenzotriazole, 5-chlorobenzotriazole, 5-nitro-benzotriazole, 4-nitro-6-chlorobenzotriazole, 5-nitro-6-chlorobenzotriazole, 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene, benzimidazole, 2-methylbenz-imidazole, 5-nitrobenzimidazole, 1-phenyl-5-mercaptotetrazole, 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptothiazoline, 2-mercapto-4-methyl-6,6′-dimethylpyrimidine, 1-ethyl-2-mercapto-5-amino-1,3,4-triazole, 1-ethyl-5-mercapto-1,2,3,4-tetrazole, 2,5-dimercapto-1,3,4-thiodiazole, 2-mercapto-5-aminothiodiazole, dimethyldithiocarbamate, and diethyldithiocarbamate.
JP 2002-293039A discloses a monochromatic or multi-colour image-forming material comprising an image-forming layer containing a dye precursor and a deblocking agent for generating the dye by reacting with the precursor of the surface of a support, wherein the deblcoking agent is a mesionic compound, but is silent in respect of the use of mesionic compounds in substantially light-insensitive thermographic recording materials whose thermosensitive element contains a substantially light-insensitive organic silver salt and a reducing agent therefor.
U.S. Pat. No. 6,306,571 discloses a process for producing an aqueous dispersion containing particles of a substantially light insensitive silver salt A, said silver salt A being a salt of a carboxylic acid having a solubility of less than 10−3 g in 100 ml of water at 20° C., said process consisting essentially of: (a) preparing an aqueous dispersion containing particles of a silver salt B, said silver salt B having a solubility of between 0.001 g and 1.5 g in 100 ml of water at 20° C., wherein the media for said aqueous dispersion is selected from the group consisting of water and mixtures of water and water-miscible organic solvents; and (b) reacting said particles of said silver salt B in the aqueous dispersion formed in step (a) with a solution of a conversion agent, wherein said conversion agent is a water soluble salt of the carboxylic acid, thereby forming the aqueous dispersion of particles of said substantially light insensitive silver salt A. U.S. Pat. No. 6,306,571 further discloses the presence of stabilizers and antifoggants in the thermographic and photothermographic materials and in an extensive list mentions the mesoionic 1,2,4-triazolium-3-thiolate precursors described in U.S. Pat. No. 4,404,390 and U.S. Pat. No. 4,351,896 and also tribromomethyl ketone compounds described in EP-A 600 587. As is explained below, one: skilled in the art would know that the stabilizing and antifoggant requirements for photothermographic materials containing a substantially light-insensitive silver salt, a reducing agent therefor and photosensitive silver halide are completely different from those for thermographic materials containing a substantially light-insensitive silver salt and a reducing agent therefor. Therefore, in respect of compounds known to stabilize photothermographic materials, such as mesoionic 1,2,4-triazolium-3-thiolate precursors and tribromomethyl ketone compounds, one skilled in the art would, in a list of stabilizers for both photothermographic and thermographic materials, associate these stabilizers with photothermographic materials and would have no expectation of stabilizing properties in respect of substantially light-insensitive thermographic materials.